In Cena's case, he became FOTC in 2005. He didn't even start to lose a match until SummerSlam 2013 against Bryan. That's alittle bit over 8 years of the same guy mowing down the roster. And this is coming off of the era in which fans were used to watching guys like Austin and Rock entertain them every week. And right after that, you go to a goody-two-shoes John Cena on top for years on end. It's not like it was even rapper John Cena. To go from Austin/Rock to the corny version of Cena, fans weren't going to stick around for that.That doesn't seem very fair to Cena. He's put over lots of guys since he started winding down his career. Bryan, Styles, Reigns, Balor, Rollins and even Fiend at Mania just a month ago. True, there was never that "passing of the torch" moment. Bryan beating him at SummerSlam 2013 was probably the closest thing to that. But, I doubt that was his call. Nonetheless, I don't think it would make too much difference in the grand scheme of things. We've had Rock endorse Reigns, we've had Rollins conquering Lesnar, we've had every legend you can think of try to crown Becky Lynch... ultimately I don't think it matters what cosigns wrestlers get from the old guard, the product just isn't exciting enough to keep people's attention. Especially when you're talking about the weekly shows, there is hardly ever anything that makes you feel like you don't want to miss next week's show. Or for people who aren't watching, there isn't anything going on that is going to make them regret missing the show. Bottom line is you're really not missing much when you skip the weekly shows. People can try to say all this shit about the Attitude Era being overrated, or not aging well, or whatever but you can't deny that they gave you a reason to tune in week after week.
And the first interesting opponents that came long for him was Nexus in 2010, and as Jericho and Edge have said, Cena buried them at SummerSlam, too, and it was very much the wrong decision. In alot of ways, it was an awful era, especially coming off an era where fans enjoyed the product so much. It was a big part of the reason I stopped watching for a few years. A few big creative decisions that went the other direction could've made the top of the card much more interesting, but it was just the same old John Cena for years and years and years. And by the time that era ended, the ratings were considerably lower than they were when they started that era. It's more on Vince than anyone else, but woof.